1. Field of the Invention
The present invention relates to a fuel cell stack.
2. Description of the Related Art
A fuel cell, for example a solid polymer electrolyte fuel cell, is formed by an MEA (membrane-electrode assembly) that is sandwiched between separators. A module is formed of at least one unit fuel cell, and the stacking of a plurality of modules (the stacking direction being arbitrary) forms a fuel cell stack. In generating electricity with a fuel cell stack, the distribution of water content may become uneven in the cell stacking direction, and result in a voltage reduction due to flooding at the stack location where excess water has collected. As a corrective measure, the Japanese Patent Application Publication No. JP-A-2004-179061 indicates the end part of the stack in the stacking direction, opposite the gas supply end, is a location that is easily flooded (with excess water), and proposes placing one of a “cell in which flooding does not easily occur,” a “cell capable of maintaining a high electrical generation efficiency even if flooded,” or a “cell having tolerance to flooding” or the like, at the end opposite the gas supply end or at both ends of a stack, this cell having performance that is different from other cells.
In the above-noted constitution, however, there is the following problem.
In actuality, it is not known what part of the stack is prone to flooding. In JP-A-2004-179061, the end of the stack in the cell stacking direction that is opposite the gas supply end is indicated as a location that is prone to flooding (with excess water). However, the end of the stack opposite the gas supply end may not be the location where water tends to accumulate. Therefore, in such case, even if a cell with good water drainage property is disposed at the end of the stack opposite the gas supply end, the flooding is not suppressed.
The identification of the location in the stack (or at which stack end) where water tends to accumulate must be determined experimentally, and is troublesome.
If cells having good water drainage property are disposed at both ends of a stack to accommodate so that the flooding is suppressed regardless of the location of the end of the stack, at which water tends to accumulate, there is a cost problem because cells having good water drainage property are expensive.